This invention relates to display apparatus.
The invention is more particularly concerned with apparatus for displaying a digital value.
Display apparatus are known in which a number is represented by energizing selected ones of a matrix array of light-emitting, light-reflecting or light-absorbing elements. The elements may typically be light-emitting diodes or liquid-crystal elements. One form of such a display is described in the specification of U.S. Pat. No. 4,240,074. Instruments for indicating the value of two or more input variables may use such a display, the same display being switched between the different input variables. In order to distinguish between the different inputs, and to show with which input variable the value displayed is associated, it is common practice to reveal an appropriate legend in the display area. Alternatively, the switch used to select which input value is displayed may be suitably marked to distinguish between the different input variables. Thus, for example, in a timepiece capable of displaying both time and date, the display might have a panel bearing the legend DATE which is revealed only when the appropriate date switch is actuated on the timepiece.
This form of display can be satisfactory in certain circumstances but is less desirable where the display must be capable of being read rapidly, at a glance, since the associated legend or marking may take a significant time to locate and read. There is also the disadvantage, where the legend is provided in the display area itself, that the area of display required for the legend leads to an increase in the overall size of the display, or a reduction in the area of display devoted to representing the value of the input variable. These disadvantages can be important, especially in application in, for example, aircraft.